1. Field of the Invention
The invention relates to a method for on-site connection of two transmission cables comprising optical fibres, each cable having a protective enclosing a central core formed with regularly spaced grooves over its periphery, each groove holding a fibre provided with a thin sheath of uniform thickness.
Cable connections of the aforementioned kind are made when a complete transmission line is first laid (allowing for the limits to the length of the sections imposed by the storage, transport and handling conditions) or during the repair of lines already in service. They have to satisfy a number of essential conditions, as follows:
They must be easy to make on site, usually in a trench, in spite of the great fragility of the fibres;
The connections must be rigid and stable over a long period irrespective of variations in temperature, humidity, etc., and
The resulting "insertion losses" on each track must be as small as possible.
2. Description of the Prior Art
U.S. patent application Ser. No. 744,595 filed Nov. 24, 1976 in the names of the present Applicants describes a method entitled "A process and apparatus for connecting cables comprising optical fibres, the position of the sections being located" whereby the cable sections are provided with connecting terminals in the factory, i.e. before being transported to the site. This system has the disadvantage of not being applicable either to repairs or to cases in which the terminals have an unacceptable bulk.
U.S. Pat. No. 3,969,015 in the name of "G. le NOANE" dated July 17, 1975 describes a system entitled "A connector for transmission cables comprising optical fibres" wherein use is made of half-connectors each comprising at least one deformable core formed with apertures for the fibres and a similarly apertured rigid piston bearing on the core so as to deform it and hold the fibres in position. This system has the disadvantage of being workable only where there is plenty of space, e.g. at stations.
Other known connections systems are supposed to be workable on site but practically all have the following disadvantages:
The fibres to be removed from the sheath which is an extremely delicate operation;
After removal from the sheath, there is a serious risk that the fibres will be broken, which complicates the operations of preparing the end surfaces of the fibres;
The insertion, positioning and securing of the thus-prepared bared fibres in centering components involve new risks of breaking and difficulties of all kinds; and
The corresponding solutions are mechanically complicated and expensive.